The present invention relates to a system for constructing space frames and, more particularly, to a modular system including hubs in combination with cylindrical tubes or struts which can be used to make simple, lightweight structures which are easily assembled.
Space grid and frame structures have long been used in architectural and engineering projects. Such structures are popular because of the repetitive nature of the design, wherein a basic geometric configuration is used. A base module is used repeatedly simply by adding more joints and connecting members to create a structure of a particular shape. The traditional space frame and grid structure comprises a grid of intersecting members forming a pattern of triangles which imparts rigidity and structural integrity to the grid. The use of rigid hubs, usually in the form of a ball with axial tapped holes in rectangular, orthoganal and hexagonal directions, is a consequence of the commitment to mathematical modeling and geometric regularity. Using the minimum number of triangular patterns minimizes the number of different angular relationships and tube lengths, so that the same type of hub may be used repeatedly throughout the structure. For example, the German "Mero" and "Meroform", and the American "Unistruct" are well known systems in which the cylindrical tubes or struts are rigidly connected at a particular angle relative to a static joint. Such systems are limited in that they provide no flexibility for adjusting the central converging angle of the struts in bridging of a static joint. As a result, the possibilities of forming geometrical patterns are limited.
An object of the present invention is to provide a universal static hub which ha maximum flexibility in joining and securing cylindrical tubes or struts to such a hub in constructing decorative frameworks.
Another object of the invention is to provide a flexible joint in a structural framework which has the ability to generate all forms of geometric configuration, both curved and planar.
Yet another object of the invention is to provide an assembly which is neat and simple, and to provide an assembly in which bolts are not required.
Still another object of the invention is to provide a static hub in which up to 18 struts may be connected.
A further object of the invention is to provide a decorative framework in which the geometric patterns may differ and which, therefore, is usable to enclose irregular spaces.
These and other objects and advantages of the invention are achieved with a modular system which includes a crystal-like static hub which may have one or more planar arrays of interconnected trunnions. In one embodiment, the trunnions are arranged to form a generally octahedral-hexagonal prism. The prism is formed by joining two hexagonal planar arrays of trunnions, each array having six nodes. The trunnions of the crystal-like hub are engaged by end grips which are attached to opposite ends of tubular members or struts. The end grips have a C-shaped section which clips into engagement with a trunnion. The C-shaped section has flat end surfaces which abut the nodes at the opposite ends of the trunnion to which the end grip is attached. The end grip is axially fixed to the strut, but free to rotate about the axis of the strut. The crystal-like hub can be used to attached up to 18 such end grips. Since the end grips are free to rotate about the trunnion, and since the struts are free to rotate about the end grips, a wide variety of angular relationships can be used to create structures of a nearly infinite variety of configurations.